1. Field of the Invention
This invention relates to a glass edge insulating unit and a method of and apparatus for making same by welding edges of glass sheets and, more particularly, joining by fusion edges of a pair of glass sheets, at least one of which has an electroconductive coating.
2. Discussion of the Prior Art and Technical Limitations of Present Technology
Insulated glass units include a pair of glass sheets spaced from one another to provide an airspace therebetween. The edges of the glass sheets are sealed using a moisture-resistant adhesive, or by welding the edges of glass sheets together. To enhance the insulating value of the units, in many instances, one of the glass sheets has a coating applied to one of the surfaces to reflect energy in selected wavelengths, for example, reflective coatings of the type taught in U.S. Pat. Nos. 4,610,771; 4,113,599 and 4,512,864. A characteristic of such coatings is that they are electroconductive. Insulated glazed units having an electroconductive coating on a sheet are easily made using processes that include the use of an adhesive to seal the space between the glass sheets, e.g. as taught in U.S. Pat. No. 4,622,249. However, such units are not easily made using processes that include moving electrical current along the sheets during fusing of the edges of the glass sheets together.
More particularly, in the process of manufacturing glass edge insulating units, for example, as taught in U.S. Pat. No. 4,132,539, which teachings are hereby incorporated by reference, a pair of glass sheets are washed and dried. In general, an electrically conductive stripe is deposited on the upper surface of the upper sheet to form a continuous electrical path around the marginal edge portions of the sheet. The sheets are assembled one on top of the other, preheated and moved into a welding chamber. A plurality of electrodes, preferably placed at the corners of a rectangular glass sheet, direct the flow of electric heating currents through selected portions of the stripe. The Portions of the upper sheet underlying the continuous stripe are heated by the current flowing through the stripe until the glass obtains a temperature at which the stripe burns off, and the glass becomes electrically conductive. The heating currents now flow through the heated marginal edges of the upper sheet.
The corresponding marginal edges of the lower sheet are heated by their close association with the heated marginal edges of the upper sheet to temperature at which the marginal edge of the lower sheet becomes electrically conductive. Heating by passing electrical currents through the heated marginal edges of the sheets is continued until the marginal edges of both sheets are softened and run together to form a continuous peripheral weld uniting the assembled sheets. Thereafter, the sheets are pulled apart while air is moved in a known manner through a hole in one of the sheets, i.e., a pore hole, into the airspace between the sheets to bloom the edges of the unit.
The unit is annealed, an insulating gas is moved into the airspace through the pore hole, and the pore hole is sealed.
The process described above for joining marginal edges of glass sheets is acceptable provided neither of the glass sheets has an electroconductive coating. In the instance where one or both of the sheets has an electroconductive coating, the current moves through the stripe, through the electroconductive coating to heat the body of the sheet. The heat is not concentrated at the marginal edges of the glass sheets; the entire sheet is heated and at high temperatures fuses to the sheets together. Further, the electroconductive coating may be damaged due to carrying the high currents needed to soften glass.
It would be advantageous therefore, to provide a process of and apparatus for welding the edges of glass sheets together when at least one of the sheets has an electroconductive coating.
U.S. Pat. No. 4,350,515 teaches a technique for making a glass edge insulating unit having an airspace of 1/2 inch (1.27 centimeter) or greater. In general, the marginal edges of a pair of glass sheets, are heated as previously discussed. After the edges are joined to form a continuous weld and electric heating discontinued, the sheets are pulled apart and held in a fixed spacial position for a period of time. Thereafter the sheets are drawn further apart until the unit has an airspace of about 1/2 inch (1.27 centimeter). The delay in the draw is practiced to obtain sidewalls of substantially uniform thickness.
As can be appreciated, it would be advantageous to provide another technique, not taught by the practice of the presently available processes, for making a glass edge insulating unit having an airspace of about 1/2 inch (1.27 centimeter) or greater and sidewalls of substantially uniform thickness.